Your power VS tyre width ratio

[jon-]

Re-watched the Harris "C63 on space savers" video last night, and it got me wondering what is the worst (best) tyre VS power ratio? ( http://www.youtube.com/watch?v=HPh90yNX-mY ), and what do we all have?

His claim of the C63 AMG being one of the best was based on:

480bhp / (255*2) wide tyres = 0.94bhp per MM.
368 lb/ft / (255*2) = 0.72 lb/ft per MM.

Only the driven wheels count. We should categorise super exotics separately from sub 100k cars.

My M3 has 358 / 255, so a lowly 0.7 bhp/MM. Something like a supercharged VX8 must be in with a good shout?

Edited for Mike.

Edited by jon- on Tuesday 11th December 10:35

[Mr2Mike]

jon- said:

His claim of the C63 AMG being one of the best was based on:

480bhp / 255 wide tyres = 1.88bhp per MM.

Shouldn't that be 480/(255*2) = 0.94 bhp/mm as there are two driven wheels?

[Ozzie Osmond]

I hope Harris did the "wet road" sums as well.

Wide tyres can be pretty exciting with a powerful car on a wet road.

[jon-]

Mr2Mike said:

jon- said:

His claim of the C63 AMG being one of the best was based on:

480bhp / 255 wide tyres = 1.88bhp per MM.

Shouldn't that be 480/(255*2) = 0.94 bhp/mm as there are two driven wheels?

Lets not make this too complicated

[Truckosaurus]

Mr2Mike said:

Shouldn't that be 480/(255*2) = 0.94 bhp/mm as there are two driven wheels?

I might be the loser here (in the 'car' category, I'm sure there are trucks/4x4s that are worse)

Volvo V60 1.6d R-Design (small engine, big wheels)

235/40R18 and 115bhp

gives 115 / (235x2) = 0.25 bhp/mm

ETA: I don't even know if I have traction control as I haven't managed to spin the wheels yet.

[papercup]

Well, the RX7 has 520bhp and 530ft/lb and runs a 255 at the rear.

520bhp / 255 wide tyres = 2.04bhp per MM

530 lb/ft / 255 tyres = 2.08 lb/ft per MM

Its quite lively.

[threesixty]

295/510 = 1.73Bhp/mm

[rj1986]

'07 X5.
231 BHP and 315/35

So that's 231/630=0.37

Where did i put DMS's number??

Edited by rj1986 on Tuesday 11th December 10:35

[Captain Muppet]

Both my cars have 160bhp, one uses 185 rear tyres, the other is currently on 235 (up from the standard 225).

MX5 Turbo: 0.865bhp/mm
Elise 160: 0.681bhp/mm (0.711bhp/mm standard)

My old 535 was 0.974bhp/mm

The one with the middle score is the only one that ever has traction problems. Odd.

[Cheburator mk2]

Mr2Mike said:

Shouldn't that be 480/(255*2) = 0.94 bhp/mm as there are two driven wheels?

i agree

mine is 0.92bhp/mm

507bhp and 275 rears

[kambites]

Surely it should be power/weight/tyre width? Absolute power means nothing. Plenty of low-powered Caterhams, etc. out there that can light up their rear wheels easily enough.

Edited by kambites on Tuesday 11th December 10:39

[Captain Muppet]

threesixty said:

295/510 = 1.73Bhp/mm

Your maths is upside down, but your result is right

[MondeoMan1981]

I used to have a Fiesta with 195s and 68bhp = 0.34 !

Just changed the car so its now 0.79 at the front and 0.72 rear !

[TVR Tommy]

TVR T350
342 / (235*2) = 0.73

Landrover 90
80 / (265*4) = 0.07

Edited by TVR Tommy on Tuesday 11th December 20:11

[darren f]

kambites said:

Surely it should be power/weight/tyre width? Absolute power means nothing. Plenty of low-powered Caterhams, etc. out there that can light up their rear wheels easily enough.

Indeed, some interesting results-

C63 AMG: 256bhp per T / 2x255mm = 0.50
Caterham Roadsport (1.6 Sigma) 227bhp per T / 2x185mm= 0.61
Caterham R500: 520bhp per T / 2x215mm = 1.21

The C63 should be on some 155s

[jimxms]

450bhp/(225*2) = a nice round 1bhp/mm

or 2bhp/mm the way that others seems to be calculating it.


Can we also factor in wheel circumference, tyre pressure and the contact patch on the floor?

Edited by jimxms on Tuesday 11th December 12:06

[s_zigmond]

BHP 300 /(2*215) so only .7
But LbFt 400/(2*215) = .93

[Parsnip]

289/245

1.18 BHP/MM

Didn't notice the edit to two tyres, half that then to .59

[shirt]

jeep on imperial tyres:
190/317.5 = 0.6bhp/mm

not as bad as i thought. Only wish those 190horses weren't so bloody lame!

[J4CKO]

I would love to contribute to this thread but I have to go and collect my anorak from the dry cleaners, I managed to get my Egg butty on it when I was out spotting buses.