tyre size

[gsx600]

What size tyres were fitted to the 400se as original fitment

225 55 15
225 50 15

or something else, as trying to match the roll diameter on my rear 16 to keep the speedo as accurate as possible

[grahamw48]

225.50 x 15.

[TVRleigh_BBWR]

Oh and they was Bridgestone RE71's if you want to get very Anal

[gsx600]

Pah wouldn't touch them !

Much better with my white walled firestones

[rev-erend]

grahamw48 said:

225.50 x 15.

What he said..

[TVRleigh_BBWR]

I'm sure 235/45 16's will give you very close rolling radius to the 225/50 15's

[gsx600]

Yep they is about the closest and wont foul on the rear tie bar either hopefully. I was hoping to get away with 235 50 16 as for a more comfortable ride !

[rev-erend]

Here a gear calculator..

http://www.gearboxman.co.uk/inforatios.html

225/50 * 15 gives a rolling Radius of 6.25 feet

235/45 * 16 gives 6.36
225/50 * 16 gives 6.51
225/45 * 16 gives 6.28

Whether you can get the sizes are another matter..

Edited by rev-erend on Monday 23 March 16:58

[gsx600]

Got a spread sheet at home , that does , rolling ratio, top speed per gear at max revs etc,

Do I go for 168 with mondeo acceleration or

a measly 155 mph with 0 - 60 times of oh my G%%

[grahamw48]

Well, since average speed on our great uprated road system now seems to be about 30mph, I'd go for 0-60 in 2.5 secs with 100mph top speed.

Reminds me of my old Seven...with wheelspin practically up to max.

[gsx600]

Take your pick, probably need to put back to excel to see it properly

But first line is standard for the 400, a theoretical 151.9 mph before engine says no

Required tyre circumference in inches 74.95 Enter Transmission details
Max Revs Diff ratio
6000 3.54
3.32 2.09 1.4 1 0.792
Tyre size Aspect Rim Diam (mm) Circum (mm) Diam (in) Circum (in) % diff Rev/mile 1st Gear 2nd Gear 3rd Gear 4th Gear 5th Gear

225 50% 15 606 1904 23.9 74.95 0% 845.33 36.2 57.6 85.9 120.3 151.9
225 55% 15 628.5 1974 24.7 77.74 4% 815.07 37.6 59.7 89.1 124.8 157.5


225 55% 16 653.9 2054 25.7 80.88 7% 783.41 39.1 62.1 92.7 129.8 163.9
225 50% 16 631.4 1984 24.9 78.09 4% 811.32 37.8 60.0 89.5 125.3 158.3
225 45% 16 608.9 1913 24.0 75.31 0% 841.30 36.4 57.8 86.3 120.9 152.6
225 40% 16 586.4 1842 23.1 72.53 -3% 873.58 35.1 55.7 83.2 116.4 147.0


235 55% 16 664.9 2089 26.2 82.24 9% 770.45 39.8 63.2 94.3 132.0 166.7
235 50% 16 641.4 2015 25.3 79.33 6% 798.67 38.4 60.9 90.9 127.3 160.8
235 45% 16 617.9 1941 24.3 76.42 2% 829.05 36.9 58.7 87.6 122.7 154.9
235 40% 16 594.4 1867 23.4 73.52 -2% 861.83 35.5 56.5 84.3 118.0 149.0


245 55% 16 675.9 2123 26.6 83.60 10% 757.91 40.4 64.2 95.8 134.2 169.4
245 50% 16 651.4 2046 25.6 80.57 7% 786.41 39.0 61.9 92.4 129.3 163.3
245 45% 16 626.9 1969 24.7 77.54 3% 817.15 37.5 59.5 88.9 124.5 157.1
245 40% 16 602.4 1892 23.7 74.51 -1% 850.38 36.0 57.2 85.4 119.6 151.0

[grahamw48]

What speed is 'rotation' ?

I wonder how the Yellow Racer was geared for long straight tracks, and what its top speed was...plus aerodynamics aids to keep it on the ground ?

[TVRleigh_BBWR]

wow that's strange I only did the same spread sheet a few days ago, see Diff thread.

Also with the yellow racer, you are assuming it was limited to 6000 RPM

at 6500 your upto 164 and 7000 your at 176, Im sure the Rv8 Tuscans would do 7000 RPM easy.

Also your calculations like mine are a bit basic, as I think you get a variance with tyre squish and other factors.

I've done some tests on the Audi, comparing GPS MPG v RPM calculated speed, and there's about 5% - 10% difference.
I'm not 100% sure I have all the ratio's correct though.

Once I have the Racer on the track, and have The Race Tech GPS logger fitted, plus digital RPM data, and Exact tyre size's I'll do some more calculations, Esp as the Racer has a 400SE Gearbox, Diff, drive shafts and 225 / 50 15 Tyres.

I'll only do the Calc's in 4th so there is no gearbox ratio's to worry about.

[JR]

gsx600 said:

Got a spread sheet at home , that does , rolling ratio, top speed per gear at max revs etc,

Do I go for 168 with mondeo acceleration or

a measly 155 mph with 0 - 60 times of oh my G%%

It also depends on which rear diff you have. I had the 28mph tall diff on my 350 giving a 168mph top speed at a nominal 6,000 red line or 217mph at the 7,750 max revs. It is of course necessary to ignor all wind resistance and the fact that the engine may blow up.

The most popular size to fit on 16" wheels is 245/45.

[TVRleigh_BBWR]

JR said:

gsx600 said:

Got a spread sheet at home , that does , rolling ratio, top speed per gear at max revs etc,

Do I go for 168 with mondeo acceleration or

a measly 155 mph with 0 - 60 times of oh my G%%

It also depends on which rear diff you have. I had the 28mph tall diff on my 350 giving a 168mph top speed at a nominal 6,000 red line or 217mph at the 7,750 max revs. It is of course necessary to ignor all wind resistance and the fact that the engine may blow up.

The most popular size to fit on 16" wheels is 245/45.

I think all the 400SE was fitting with the 3.54 diff giving the max figures posted above. as said it not an exact sicence, also wind resistance should not affect MPH per RPM, unless the drag is causing diff or clutch slip.

You can get 3.31 and 3.07 Diff's which will give you a higher top speed. but not sure if these have limited slip.

[JR]

TVRleigh_BBWR said:

JR said:

gsx600 said:

Got a spread sheet at home , that does , rolling ratio, top speed per gear at max revs etc,

Do I go for 168 with mondeo acceleration or

a measly 155 mph with 0 - 60 times of oh my G%%

It also depends on which rear diff you have. I had the 28mph tall diff on my 350 giving a 168mph top speed at a nominal 6,000 red line or 217mph at the 7,750 max revs. It is of course necessary to ignor all wind resistance and the fact that the engine may blow up.

The most popular size to fit on 16" wheels is 245/45.

I think all the 400SE was fitting with the 3.54 diff giving the max figures posted above.

The figures that I have quoted are for tall gearing. Standard gives about 25mph/1,000 rpm in top as per:

gsx600 said:

But first line is standard for the 400, a theoretical 151.9 mph before engine says no

Required tyre circumference in inches 74.95 Enter Transmission details
Max Revs Diff ratio
6000 3.54
3.32 2.09 1.4 1 0.792
Tyre size Aspect Rim Diam (mm) Circum (mm) Diam (in) Circum (in) % diff Rev/mile 1st Gear 2nd Gear 3rd Gear 4th Gear 5th Gear

225 50% 15 606 1904 23.9 74.95 0% 845.33 36.2 57.6 85.9 120.3 151.9

[TVRleigh_BBWR]

What is the ratio for tall gearing though.

[grahamw48]

I'm assuming the various diffs originate from Jag XJ6/12 and variants of that drivetrain. The XJS was based on a shortened floor pan, but basically similar mechanicals.

If so, that is where you need to be looking for your facts and figures regarding diff ratios. (Only wish I hadn't thrown out my Jag manuals. ). Perhaps an exploration of the Jag owners website ?

eta... found some interesting stuff on here:

http://search.jag-lovers.org/search04/index.php

just put 'diff ratios' in the search.

Edited by grahamw48 on Tuesday 24th March 22:04