Hybrid_From_Hell Posted November 21, 2005 Share Posted November 21, 2005 Please can some kind soul(s) measure the overall circumference of the tyres below .... a 205 x 16 a 7.50x 16 Please, inches or MM either would be jolly fine Nige Quote Link to comment Share on other sites More sharing options...
landrover598 Posted November 21, 2005 Share Posted November 21, 2005 (edited) diameter a 720mm b 780mm Edited November 21, 2005 by landrover598 Quote Link to comment Share on other sites More sharing options...
Hybrid_From_Hell Posted November 21, 2005 Author Share Posted November 21, 2005 (edited) Thankyou !..... Nige er .....................having looked and played I actually need circumference !!!!!!!!!!!!!1 Nige Edited November 21, 2005 by Hybrid_From_Hell Quote Link to comment Share on other sites More sharing options...
darthdicky Posted November 21, 2005 Share Posted November 21, 2005 Circumference = Diameter x Pi so using Daves figures 205x16 = 2261mm 750x16 = 2450mm Divide by 25.4 to get inches. Richard Quote Link to comment Share on other sites More sharing options...
Hybrid_From_Hell Posted November 21, 2005 Author Share Posted November 21, 2005 Ta.... Anyone got a 235 85 x 16 they could measure around please !! Nige Quote Link to comment Share on other sites More sharing options...
landrover598 Posted November 21, 2005 Share Posted November 21, 2005 2482mm Quote Link to comment Share on other sites More sharing options...
SteveG Posted November 21, 2005 Share Posted November 21, 2005 Ta....Anyone got a 235 85 x 16 they could measure around please !! Nige Hi Nige Click here, enter site and clickon tyre info, there's a tyre calculator at the bottom of the page http://www.slroc.com Cheers Steve Quote Link to comment Share on other sites More sharing options...
BogMonster Posted November 21, 2005 Share Posted November 21, 2005 Nige There are quite big differences between different brands of tyre Sit a 7.50R16 Michelin XS against a 7.50R16 Avon Rangemaster to see what I mean.... ....probably about an inch difference in the height! maybe a bit more (don't have them handy to check but side by side you would never believe they were the "same size") so a lot of the measurement depends on what sort of tyre you are using - and I think 7.50R16 is a "particularly variable size" - the metric sizes are more accurately specified - 205R16 is actually 205/80R16 and they shouldn't vary quite so much Quote Link to comment Share on other sites More sharing options...
Ex Member Posted November 21, 2005 Share Posted November 21, 2005 I guess I should ask why? If you are trying to figure out gearing, this measurement is of no use. You need loaded radius. Quote Link to comment Share on other sites More sharing options...
Hybrid_From_Hell Posted November 21, 2005 Author Share Posted November 21, 2005 John, The program I have works out speed at given 500 rpm jumps up to a preset max. It does it for all gears and low and high box, and needs 1/2/3/4/5th Ratios, Diff Ratio, Circumference of tyre, and TBox Ratio... I have worked out that I am approx 20% higher geared than a factory V8 on 205s, and slightly less if on 7.50s / 235s. With the V8 it dioes sort of overcome the extra gearing, but it is a step maybe too far, and I think 1.222 will stay and I'll if I do change much will do P&Ps, On a run 5th is a struggle up a moderate hill !, its since the simexs went on , it was fine on 7.50s / 235 grizzlys... Nige Quote Link to comment Share on other sites More sharing options...
Ex Member Posted November 21, 2005 Share Posted November 21, 2005 Yes, but the inflated circumference of the tyre will not give the correct values. You need the rolling radius or rolling circumference which is quite bit smaller. Quote Link to comment Share on other sites More sharing options...
LR90 Posted November 21, 2005 Share Posted November 21, 2005 On a run 5th is a struggle up a moderate hill !, its since the simexs went on , it was fine on 7.50s / 235 grizzlys...Nige That's 34" Simex, 300BHP and it struggles on a MODERATE hill No wonder I need LT77 (0.830), LT230 (1.192), 4.7 R&P (4.75 wanted) and 35" Simex to match my bog std TDi. Did go to measure some tyres (got 205s, 7.50 SAGs and 7.50 XS stacked in the garage) but its cold, dark and I'm going to have to pull them all out to get a tape round them. Quote Link to comment Share on other sites More sharing options...
Hybrid_From_Hell Posted November 21, 2005 Author Share Posted November 21, 2005 (edited) Yes, but the inflated circumference of the tyre will not give the correct values. You need the rolling radius or rolling circumference which is quite bit smaller. Yep, but WTF am I going to get those ! I have looked at my Simex 34s, they are (off the 90) 107.5 inches circumference, versus the 7.50s 235s, and 205 etc, would you think the percentage difference of circumference versusus rolling circumference would be reasonable similar say 5-7% ?.......... Nige Edited November 21, 2005 by Hybrid_From_Hell Quote Link to comment Share on other sites More sharing options...
Ex Member Posted November 21, 2005 Share Posted November 21, 2005 If you go to BFGs site, they list revolutions per mile for all of their tires. That gives you the data you need, but as stated, different brands vary. http://www.bfgoodrichtires.com/bfgapp/index.jsp Lots of sizes shown here 235/70/16: 712 revs/mile 235/85/16: 650 revs/mile 285/75/16: 628 revs/mile 35x12.5x15: 598 revs/mile Quote Link to comment Share on other sites More sharing options...
Ex Member Posted November 21, 2005 Share Posted November 21, 2005 If you measure the loaded radius carefully, you can estimate the rolling circumference. Measure from the ground to the center of the drive member (on a flat surface). Multiply this by 2 and then by pi to get the rolling circumference. A better way is put a mark on the side of the tyre where is touches the road and on the road. Have someone drive slowly forward and count out say 5 revolutions. Measure the road distance travelled. Make sure the road is fairly smooth and flat, say a parking lot. Quote Link to comment Share on other sites More sharing options...
Turbocharger Posted November 22, 2005 Share Posted November 22, 2005 If you measure the loaded radius carefully, you can estimate the rolling circumference. Measure from the ground to the center of the drive member (on a flat surface). Multiply this by 2 and then by pi to get the rolling circumference. What about the "caterpillar track" effect? A better way is put a mark on the side of the tyre where is touches the road and on the road. Have someone drive slowly forward and count out say 5 revolutions. Measure the road distance travelled. Make sure the road is fairly smooth and flat, say a parking lot. You'll actually get less than this on the road though because of rotational slip under power... You could work it out with GPS and an accurate tachometer... but for the purposes here the %age change ought to be the important bit - the actual ratio is academic. Quote Link to comment Share on other sites More sharing options...
02GF74 Posted November 22, 2005 Share Posted November 22, 2005 Ta....Anyone got a 235 85 x 16 they could measure around please !! Nige I can measure rolling radius for an extremely low mileage 235/85 R16 General Tire MT is you want as fitted to a lightly loaded LWT if you still need such info. Quote Link to comment Share on other sites More sharing options...
Diff Posted November 22, 2005 Share Posted November 22, 2005 Hi Nige, I have used the calculator on this site to very good effect: http://www.4lo.com/calc/gearratio.htm Just put the tyre diameter in inches. Whilst it does not take into account differences between different brands of the same tyre, it is very useful for comparing between sizes and if comparing effects of different transfer ratios with the same size tyres. For the purposes of the discussion my 235/85 X 16 Hankook MT tyres are 32.5 inches in diameter (102.05 inches circumference) compared to a dunlop 7.50x16 which measures 32 inches diameter(100.48 inches circumference). Hope this helps, Regards, Diff Quote Link to comment Share on other sites More sharing options...
Mark90 Posted November 22, 2005 Share Posted November 22, 2005 http://www.mark-90.pwp.blueyonder.co.uk/gearbox.xls may help in perforning calculations, just edit the blue figures and see what happens to the red ones. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.