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 Post subject: Dolomite Sprint Tyres
PostPosted: Sat Apr 09, 2022 3:36 pm 
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Hello!

My 1978 Sprint requires a new set of tyres as the current Dunlop SP Sport 200s are 12 years old and starting to show their age. When I last replaced them, the correct H-rated tyres were fairly easy to find but not so much now! T-rated tyres from Toyo, Continental and Yokohama seem plentiful and fairly inexpensive, yet H-rated ones are hard to find and very expensive! There are a few weird names I've never heard of before, then the Pirelli CN36 Cinturato at £130/corner (albeit a beautiful looking tyre!).

I was wondering what people would recommend for both a decent-performing and classic-looking tyre? Is it okay to use a lower speed rating considering I am very unlikely to be going over 118MPH that the T rating covers?

Thanks in advance!

Howard

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1966 Volkswagen 1300 (project thread)
1962 Austin Mini (project)
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PostPosted: Sat Apr 09, 2022 4:00 pm 
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In my opinion T rating is more than adequate unless you want to do serious track laps etc.
I run Falken Sincera SN832 Ecorun on the Spitfire - excellent grip and I highly recommend them if they are cost effective in the size you are looking for.

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PostPosted: Sat Apr 09, 2022 5:36 pm 
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Hello
Good to see you still have your Sprint Howard!
Seems ages since you have been on here?


Sorry, cannot help with an answer to your question, because
I have went for 14” wheels (with a better offset(ET25)) myself



Ian

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PostPosted: Sat Apr 09, 2022 10:46 pm 
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Another vote for the T rated Falkens. I've used them on several customer cars to date and had nothing but good reports back. They perform well and seem to last too.

H rating is a rather optimistic 130mph, not many will want (or be able) to exceed the T rating's 118mph! Note that the T rating wasn't available in the 70s, there was only S (112mph) H (130mph) and V (145mph IIRC)

TBH, with the Sprint's brick-like aerodynamics, I'm not convinced it's physically possible! The Carledo, with 140+ bhp on tap and severely lightened, with a power to weight ratio of 175bhp/tonne can only just about reach a true 115mph with a couple of miles to wind up! Still had only 5200 rpm on the tach at that speed, redlined at 6500 and limited at 7200rpm so plenty of revs left, just beaten by the aero, or lack thereof!

Steve

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'78 Sprint Auto with Vauxhall Omega 2.2 16v engine (The Dolomega)
'72 Triumph 1500FWD in Slate Grey, Now with RWD and Carledo powertrain!

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PostPosted: Sat Apr 09, 2022 11:14 pm 
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TBH, with the Sprint's brick-like aerodynamics, I'm not convinced it's physically possible!

Steve
Ask Darren Faulkner!


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PostPosted: Sun Apr 10, 2022 8:20 pm 
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Good to see you still have your Sprint Howard!
Seems ages since you have been on here?
Thanks Ian, and yes, I most definitely still have my Sprint, I've had her 14 years now so selling is not an option! She was ultimately taken off the road in 2018/19 pending some major maintenance issues, which I never had the time, money or enthusiasm to sort out as most of that was used up by my Spitfire, which as lovely as that car was, has now gone to a new home and replaced with something more modern*. Then COVID hit... so she's sat for a while. Having recently got my mojo back, I've recently rehung the exhaust, replaced the front brake callipers, overhauled the carburettors for E10, replaced the throttle linkage and am currently partway through a water pump replacement (and engine bay tidy up while everything is accessible). Plan is to hopefully get the car back in tip-top condition for the shows this year, and if all goes to plan the RBRR next year...

All will be detailed in the restoration thread soon :)

*"Modern" being a 2001 Rover 25 2.5-litre V6 :lol:

Howard

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1978 Triumph Dolomite Sprint (project thread)
1966 Volkswagen 1300 (project thread)
1962 Austin Mini (project)
1962 MGA 1600 Mark II
1965 Mobylette SP50 (project)
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PostPosted: Sun Apr 10, 2022 8:30 pm 
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Another vote for the T rated Falkens. I've used them on several customer cars to date and had nothing but good reports back. They perform well and seem to last too.

H rating is a rather optimistic 130mph, not many will want (or be able) to exceed the T rating's 118mph! Note that the T rating wasn't available in the 70s, there was only S (112mph) H (130mph) and V (145mph IIRC)

TBH, with the Sprint's brick-like aerodynamics, I'm not convinced it's physically possible! The Carledo, with 140+ bhp on tap and severely lightened, with a power to weight ratio of 175bhp/tonne can only just about reach a true 115mph with a couple of miles to wind up! Still had only 5200 rpm on the tach at that speed, redlined at 6500 and limited at 7200rpm so plenty of revs left, just beaten by the aero, or lack thereof!

Steve
Thanks Steve, I've heard good things about the Falkens! Although I've just come across the Yokohama ADVAN HF Type-D which is a classic tyre in the correct speed rating... and looks lovely to boot.. hmm. :lol:

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1978 Triumph Dolomite Sprint (project thread)
1966 Volkswagen 1300 (project thread)
1962 Austin Mini (project)
1962 MGA 1600 Mark II
1965 Mobylette SP50 (project)
2001 Rover 75 2.5-litre V6


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PostPosted: Sun Apr 10, 2022 9:12 pm 
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TBH, with the Sprint's brick-like aerodynamics, I'm not convinced it's physically possible!

Steve
Ask Darren Faulkner!
Well sure, add enough horses and subtract enough weight and you'll get a V-max in excess of 120mph and justify those H raters. Just how many horses is open to debate, I fancy ALG 1K has somewhere in the region of 500 disporting themselves under the bonnet and his new carbon fibre skinned car will be closer to 700. Though, TBH, I suspect that is much more than enough and 250 would do. But that is the top end of what a Sprint engine CAN produce and such cars are track monsters, not suitable for road use and never used on road tyres. Dan Brown's Turbo Nissan powered car has circa 350 horses, that should be enough. But that, like the Carledo runs on 50 profile 15s that start with a V rating anyway (and still only £50 a corner for Toyo Proxes)

Be that as it may, once you get over 100 mph, the drag coefficient is the most significant influence on performance. Bad aero and/or lots of drag stunts performance, ruins fuel consumption and will, if you go fast enough, make the car dangerously unstable. Remember those Mercedes that literally took off on the Mulsanne straight a few years go? Not sure i'd want to take my Sprint over 140, even if it was a) capable of such speed (which I doubt) and b) in a place safe and legal to do it. In any case, V-max is almost irrelevant these days, nobody but a few obsessives like Jon Jackson actually care. Acceleration is far more significant.

In my youth I drove both a Lamborghini Espada which showed me 172 mph on the clock before I chickened out and a Plymouth Superbird (theoretical v-max in the region of 210mph) which I baled on at less than 150, it scared me witless at that speed, shuddering, rattling, shaking and wandering all over the place. This car had a droop snoot AND a giant rear wing, hot stuff for 1971 but it's still beyond me how Richard Petty and his mates lapped Daytona at over 200mph in them, cojones of solid stainless steel no doubt!

Not to mention the fact that Plod will have your licence if they catch you doing over a ton on the public highway!

So NO! I still don't think the average Sprint owner is in any danger of outrunning T rated tyres. Those that are at risk of that sort of thing, are already running something better!

Steve

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'73 2 door Toledo with Vauxhall Carlton 2.0 8v engine (The Carledo)
'78 Sprint Auto with Vauxhall Omega 2.2 16v engine (The Dolomega)
'72 Triumph 1500FWD in Slate Grey, Now with RWD and Carledo powertrain!

Maverick Triumph, Servicing, Repairs, Electrical, Recomissioning, MOT prep, Trackerjack brake fitting service.
Apprentice served Triumph Specialist for 50 years. PM for more info or quotes.


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PostPosted: Sun Apr 10, 2022 9:26 pm 
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Quote:
Another vote for the T rated Falkens. I've used them on several customer cars to date and had nothing but good reports back. They perform well and seem to last too.

H rating is a rather optimistic 130mph, not many will want (or be able) to exceed the T rating's 118mph! Note that the T rating wasn't available in the 70s, there was only S (112mph) H (130mph) and V (145mph IIRC)

TBH, with the Sprint's brick-like aerodynamics, I'm not convinced it's physically possible! The Carledo, with 140+ bhp on tap and severely lightened, with a power to weight ratio of 175bhp/tonne can only just about reach a true 115mph with a couple of miles to wind up! Still had only 5200 rpm on the tach at that speed, redlined at 6500 and limited at 7200rpm so plenty of revs left, just beaten by the aero, or lack thereof!

Steve
Thanks Steve, I've heard good things about the Falkens! Although I've just come across the Yokohama ADVAN HF Type-D which is a classic tyre in the correct speed rating... and looks lovely to boot.. hmm. :lol:
I don't know this particular model, but am a big fan of Yokos, running my convertible GT6 on A008s for many years.

Stick like you-know-what to a blanket and excellent in the wet, at least twice as good as the comparable Goodyear of the time, which was much pricier. (I tried all sorts before settling on the Yokos)

Only downside was the inevitable compromise, they didn't last long, I struggled to get 10k miles from each set, which on that daily driven car meant a set every year! Still, better I suppose, to wear them out with a big silly grin on my face than have them crack and die of old age!

Steve

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'73 2 door Toledo with Vauxhall Carlton 2.0 8v engine (The Carledo)
'78 Sprint Auto with Vauxhall Omega 2.2 16v engine (The Dolomega)
'72 Triumph 1500FWD in Slate Grey, Now with RWD and Carledo powertrain!

Maverick Triumph, Servicing, Repairs, Electrical, Recomissioning, MOT prep, Trackerjack brake fitting service.
Apprentice served Triumph Specialist for 50 years. PM for more info or quotes.


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PostPosted: Mon Apr 11, 2022 4:52 pm 
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I don't know this particular model, but am a big fan of Yokos, running my convertible GT6 on A008s for many years.

Stick like you-know-what to a blanket and excellent in the wet, at least twice as good as the comparable Goodyear of the time, which was much pricier. (I tried all sorts before settling on the Yokos)

Only downside was the inevitable compromise, they didn't last long, I struggled to get 10k miles from each set, which on that daily driven car meant a set every year! Still, better I suppose, to wear them out with a big silly grin on my face than have them crack and die of old age!

Steve
Try some Falkens when the Yoko's need to be replaced. You will be surprised.

Jeroen

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PostPosted: Sun May 01, 2022 5:25 pm 
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Another vote for the T rated Falkens. I've used them on several customer cars to date and had nothing but good reports back. They perform well and seem to last too.

H rating is a rather optimistic 130mph, not many will want (or be able) to exceed the T rating's 118mph! Note that the T rating wasn't available in the 70s, there was only S (112mph) H (130mph) and V (145mph IIRC)

TBH, with the Sprint's brick-like aerodynamics, I'm not convinced it's physically possible! The Carledo, with 140+ bhp on tap and severely lightened, with a power to weight ratio of 175bhp/tonne can only just about reach a true 115mph with a couple of miles to wind up! Still had only 5200 rpm on the tach at that speed, redlined at 6500 and limited at 7200rpm so plenty of revs left, just beaten by the aero, or lack thereof!

Steve
In late-1987, I fitted French-made, T-rated, 185/70 R13 Firestone S211 M+S tyres to my 1974 Triumph Toledo 1300, on the 5.5 x 13 inch Cosmic alloy wheels (21 mm offset), which were later transferred to the substitute 5.5 x 13 inch Dolomite Sprint wheels (35 mm offset). Rated upto a maximum of 118 mph, they were rather over-rated for by 58 bhp Toledo, but I could not find and S-rated tyres by then! :cry: Owing to premature wear of the two front tyres attributable to a toe-in misalignment, I needed to replace them with South African made, T-rated, 185/70 R13 Firestone S211 M+S tyres in circa 1995. They were all still in fine fettle in mid-1999, with plenty of tread remaining, when I laid-up the car in mid-1999.

I cannot presently recall (it's probably documented in my DIY service records!) the average mileage covered by each of these 185/70 R13 Firestone S211 M+S tyres, but each of my previous set of five Kelly-Springfield Steelmark, 175 SR13 (i.e. 175/80 R13) tyres on the Cosmic wheels, lasted more than 35,000 miles of road use, from early-1982 to late-1987, before I replaced them at circa 2.5 mm tread-depth.

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PostPosted: Sun May 01, 2022 8:09 pm 
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Since when is wear a parameter?

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PostPosted: Wed May 04, 2022 12:32 pm 
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TBH, with the Sprint's brick-like aerodynamics, I'm not convinced it's physically possible!
Steve
The TR7 Sprint was supposed to top out at 120, with 0-60 in 8.5. They are the same as the specs for the 135bhp US TR8. But I don't know if the TR8 was 135 SAE or 135 DIN. Where I know the Dolomite Sprint was 135 SAE, but only 127 DIN. This does imply that German horses are stronger than American ones, but I'm not sure that's true. Perhaps they are just encouraged more efficiently.

But the TR7's plaid cloth seats may be an issue in driving it to 120 mph, as the stains will never come out.

As to how many horses to go how fast - if it's limited by aerodynamics, so rolling resistances can be ignored, and ignoring ground effect (cos the maths is too hard), it should take 8 times as many horses to make the same shape car go twice as fast: Power = Force x Velocity (Power = Work / Time; Work = Force x Distance; Velocity = Distance / Time). So 4 times the force (drag being proportional to V squared) moving at twice the V.

Graham

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PostPosted: Wed May 04, 2022 6:16 pm 
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Quote:
TBH, with the Sprint's brick-like aerodynamics, I'm not convinced it's physically possible!
Steve
The TR7 Sprint was supposed to top out at 120, with 0-60 in 8.5. They are the same as the specs for the 135bhp US TR8. But I don't know if the TR8 was 135 SAE or 135 DIN. Where I know the Dolomite Sprint was 135 SAE, but only 127 DIN. This does imply that German horses are stronger than American ones, but I'm not sure that's true. Perhaps they are just encouraged more efficiently.

But the TR7's plaid cloth seats may be an issue in driving it to 120 mph, as the stains will never come out.

As to how many horses to go how fast - if it's limited by aerodynamics, so rolling resistances can be ignored, and ignoring ground effect (cos the maths is too hard), it should take 8 times as many horses to make the same shape car go twice as fast: Power = Force x Velocity (Power = Work / Time; Work = Force x Distance; Velocity = Distance / Time). So 4 times the force (drag being proportional to V squared) moving at twice the V.

Graham
Well the 0-60 of 8.5 is close or the same as that widely advertised for the Dolomite Sprint in the UK. Non emasculated UK Tr8s (not that there were many) running on carbs probably shoved out a bit more, that V8 engine in the P6B was rated at 155bhp (DIN) slightly less in the worse breathing but much lighter MGBGTV8. But the TR7 Sprint (as a hardtop as they all were) is clearly a much cleaner shape aerodynamically so, along with a tad less weight, a V-max of 120 is a fairly reasonable assumption. The same engine in a convertible would probably struggle to make over 100mph top down or maybe 105 top up. That was my experience with my GT6 convertible in the 80s, from experiments conducted in the same place in the same car on the same day. With the (nothing special aerodynamically) Spitfire hardtop on, it showed me a true V-max of 117mph, (a "proper" GT6 MkII with the sloping tail was supposed to top out at 120) with the hardtop removed and the soft top errected it could only make 104mph where you'd think the weight loss would make it faster and top down it REALLY didn't even want to make the ton, I reckon 98 was about it's lot!

Which matches all i've learned about aero. Aerodynamic drag doesn't seem to increase linearly (is that a word?) but in a curve which is like the reverse of an engine power curve, where an engine starts off on a steep curve which tapers off towards the top, a drag curve starts off shallow and doesn't seem to really climb to significance until around 80 mph. Till, on a stock Sprint, by 110 or thereabouts, it's near vertical. Sure, with enough extra power you can overcome this resistance, you just pay the price in fuel consumption. As you so correctly pointed out, the engine needs to work harder the faster you go, it can only work so hard at max power output which gives you a V-max for any given engine in any given car shape, where power output exactly equals aero drag. Other parasitic losses are tiny by comparison , so I'm ignoring them! Add more power and the V-max will rise but the engine needs more fuel to make that extra power so fuel consumption rises, also by that 4x figure unless i've done my sums wrong. Certainly it's much more than a linear progression anyway. It's a big part of why the average car is so much more economical at 60mph than at 90, at 60, the drag curve is still fairly flat whereas at 90 it's much steeper.

Lousy as the Sprint's aero is, it could be worse! When first built, at standard Toledo ride height and sans the standard chin spoiler, the Carledo was "nervous" at 80mph or more. Dropping it an inch and a half and adding that chin spoiler made a surprisingly big difference to high speed stability.

So, in one way, by picking a Dolomite to make quicker, i'm starting in the wrong place, I should choose a body shape that is much cleaner aerodynamically. But I LIKE the shape so i'll live with it! In any case, plod will take your licence if they catch you at over a ton so, whether my V-max is 120 or 150, is really irrelevant!

As far as tyres go, even when on a trackday at Castle Coombe, there's only one spot where I can touch 100mph before braking hard for the next corner, so from a purely tyre safety point of view, I could manage comfortably on T or even the the now nearly obsolete S rated tyres and the V raters i'm using are a bit overkill!

Steve

_________________
'73 2 door Toledo with Vauxhall Carlton 2.0 8v engine (The Carledo)
'78 Sprint Auto with Vauxhall Omega 2.2 16v engine (The Dolomega)
'72 Triumph 1500FWD in Slate Grey, Now with RWD and Carledo powertrain!

Maverick Triumph, Servicing, Repairs, Electrical, Recomissioning, MOT prep, Trackerjack brake fitting service.
Apprentice served Triumph Specialist for 50 years. PM for more info or quotes.


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PostPosted: Wed May 04, 2022 6:32 pm 
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Quote:
Since when is wear a parameter?

Jeroen
WEAR has always been a PARAMETER so far as I am concerned! Not everyone has unlimited funds to run a motor vehicle and buying a complete set of five or six tyres (i.e. one or two spares), once every 6~10 years, is quite frequent enough for me! :shock: :cry:

The six Michelin XZX 185 SR14 Reinforced radial tyres (two spares) that my father had fitted in circa 1977/78 (a mere 43~45 years ago) to our 1973 VW "1600" Type 2 Westfalia Continental motor-caravan, still appear to be in good condition, but I shall give them a thorough inspection and low-speed trial before I contemplate re-using them. :wink:
Quote:
Quote:
Quote:
TBH, with the Sprint's brick-like aerodynamics, I'm not convinced it's physically possible!
Steve
The TR7 Sprint was supposed to top out at 120, with 0-60 in 8.5. They are the same as the specs for the 135bhp US TR8. But I don't know if the TR8 was 135 SAE or 135 DIN. Where I know the Dolomite Sprint was 135 SAE, but only 127 DIN. This does imply that German horses are stronger than American ones, but I'm not sure that's true. Perhaps they are just encouraged more efficiently.

But the TR7's plaid cloth seats may be an issue in driving it to 120 mph, as the stains will never come out.

As to how many horses to go how fast - if it's limited by aerodynamics, so rolling resistances can be ignored, and ignoring ground effect (cos the maths is too hard), it should take 8 times as many horses to make the same shape car go twice as fast: Power = Force x Velocity (Power = Work / Time; Work = Force x Distance; Velocity = Distance / Time). So 4 times the force (drag being proportional to V squared) moving at twice the V.

Graham
Well the 0-60 of 8.5 is close or the same as that widely advertised for the Dolomite Sprint in the UK. Non emasculated UK Tr8s (not that there were many) running on carbs probably shoved out a bit more, that V8 engine in the P6B was rated at 155bhp (DIN) slightly less in the worse breathing but much lighter MGBGTV8. But the TR7 Sprint (as a hardtop as they all were) is clearly a much cleaner shape aerodynamically so, along with a tad less weight, a V-max of 120 is a fairly reasonable assumption. The same engine in a convertible would probably struggle to make over 100mph top down or maybe 105 top up. That was my experience with my GT6 convertible in the 80s, from experiments conducted in the same place in the same car on the same day. With the (nothing special aerodynamically) Spitfire hardtop on, it showed me a true V-max of 117mph, (a "proper" GT6 MkII with the sloping tail was supposed to top out at 120) with the hardtop removed and the soft top errected it could only make 104mph where you'd think the weight loss would make it faster and top down it REALLY didn't even want to make the ton, I reckon 98 was about it's lot!

Which matches all i've learned about aero. Aerodynamic drag doesn't seem to increase linearly (is that a word?) but in a curve which is like the reverse of an engine power curve, where an engine starts off on a steep curve which tapers off towards the top, a drag curve starts off shallow and doesn't seem to really climb to significance until around 80 mph. Till, on a stock Sprint, by 110 or thereabouts, it's near vertical. Sure, with enough extra power you can overcome this resistance, you just pay the price in fuel consumption. As you so correctly pointed out, the engine needs to work harder the faster you go, it can only work so hard at max power output which gives you a V-max for any given engine in any given car shape, where power output exactly equals aero drag. Other parasitic losses are tiny by comparison , so I'm ignoring them! Add more power and the V-max will rise but the engine needs more fuel to make that extra power so fuel consumption rises, also by that 4x figure unless i've done my sums wrong. Certainly it's much more than a linear progression anyway. It's a big part of why the average car is so much more economical at 60mph than at 90, at 60, the drag curve is still fairly flat whereas at 90 it's much steeper.

Lousy as the Sprint's aero is, it could be worse! When first built, at standard Toledo ride height and sans the standard chin spoiler, the Carledo was "nervous" at 80mph or more. Dropping it an inch and a half and adding that chin spoiler made a surprisingly big difference to high speed stability.

So, in one way, by picking a Dolomite to make quicker, i'm starting in the wrong place, I should choose a body shape that is much cleaner aerodynamically. But I LIKE the shape so i'll live with it! In any case, plod will take your licence if they catch you at over a ton so, whether my V-max is 120 or 150, is really irrelevant!

As far as tyres go, even when on a trackday at Castle Coombe, there's only one spot where I can touch 100 mph before braking hard for the next corner, so from a purely tyre safety point of view, I could manage comfortably on T or even the the now nearly obsolete S rated tyres and the V raters i'm using are a bit overkill!

Steve
Not only does the engine have to develop more power to overcome aerodynamic drag (proportional to the air's relative velocity squared) but with increasing speed one also needs greater additional power (in addition to that needed to overcome rolling resistance, aerodynamic drag and change in gravitational potential energy when climbing a gradient, no matter how slight!) to maintain the same degree of acceleration, which is equal to the product of speed x acceleration x mass, which one can deduce by differentiating kinetic energy E = ½mv² with respect to time, using either the chain rule or product rule of differentiation.

_________________
Regards.

Nigel A. Skeet

Independent tutor of mathematics, physics, technology & engineering, for secondary, tertiary, further & higher education.

https://www.linkedin.com/profile/view?id=308177758

Upgraded 1974 Triumph Toledo 1300 (Toledo / Dolomite HL / Sprint hybrid)

Onetime member + magazine editor & technical editor of Volkswagen Type 2 Owners' Club


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