longsh07 Posted October 25, 2016 Share Posted October 25, 2016 (edited) So I was having a look at big brake kits and stumbled across a site which states: legally for road use rolling radius must be no more than +/- 3% from Original specification (source: https://balancemotor.../big-brake-kits) Just curious really, anyone else ever heard this before? I know best practice is to stick as close as possible to stock rolling radius and +/-3% is a rough rule of thumb to keep odometer and speedo in check but I've never heard of going over/under 3% from OEM being illegal! Edited October 25, 2016 by longsh07 1 Quote Link to comment Share on other sites More sharing options...
Ekona Posted October 25, 2016 Share Posted October 25, 2016 Utter load of b*llocks. Quote Link to comment Share on other sites More sharing options...
Ekona Posted October 25, 2016 Share Posted October 25, 2016 Or to be more precise, ask them to quote which piece of legislation they're referring to. If such a piece exists, I'll send them a Curly Wurly. Quote Link to comment Share on other sites More sharing options...
longsh07 Posted October 25, 2016 Author Share Posted October 25, 2016 I prefer your first response personally but I might drop them an email about it. Quote Link to comment Share on other sites More sharing options...
G1en Posted October 25, 2016 Share Posted October 25, 2016 http://www.motuk.co.uk/manual_410.htm Cant see anything in there. First thing that came up on google. Only states you cant have 2 different tyre sizes on same axle so unless your driving a nascar i think your fine Quote Link to comment Share on other sites More sharing options...
TT350 Posted October 25, 2016 Share Posted October 25, 2016 Or to be more precise, ask them to quote which piece of legislation they're referring to. If such a piece exists, I'll send them a CURLY WURLEY. Not seen one of those for years! Quote Link to comment Share on other sites More sharing options...
HEADPHONES Posted October 25, 2016 Share Posted October 25, 2016 When I saw curly wurly straight after the word b*llocks being mentioned, I thought Ekona was talking about sending them a pube in the post 1 Quote Link to comment Share on other sites More sharing options...
Ekona Posted October 26, 2016 Share Posted October 26, 2016 Curly Wurlys are the king of chocolate snacks. There is nothing finer, and to be awarded one is a very high achievement indeed. Quote Link to comment Share on other sites More sharing options...
longsh07 Posted October 26, 2016 Author Share Posted October 26, 2016 Apparently it's part of an MOT Hi MattStandard mot test covers this but a lot of cars get through with "wrong" tyres if all 4 are the same by all means call to discuss as there are some benefits to using a smaller rolling radius but larger rolling radius will - make speedo read slow - reduce acceleration and top speed through longer gearing - reduce brake effectiveness Sent from my HTC One M9 using Tapatalk Quote Link to comment Share on other sites More sharing options...
Ekona Posted October 26, 2016 Share Posted October 26, 2016 As I said, utter b*llocks. Nowhere in the MOT manual does it state that silly 3% rule, and even if it did it wouldn't make it illegal. It's not illegal for me to have fluffy dice in my car. It will fail an MOT. It is illegal to drive round without an MOT. That doesn't make fluffy dice illegal. 1 Quote Link to comment Share on other sites More sharing options...
rabbitstew Posted October 26, 2016 Share Posted October 26, 2016 It's not illegal for me to have fluffy dice in my car. It will fail an MOT. It is illegal to drive round without an MOT. That doesn't make fluffy dice illegal. My head hurts... Quote Link to comment Share on other sites More sharing options...
Ekona Posted October 26, 2016 Share Posted October 26, 2016 What I'm saying is that there is no explicit law saying that fluffy dice are illegal. There is a section in the MOT that deals with obstructions to view, and that's why fluffy dice will fail an MOT, but that doesn't mean it's illegal for me to put them straight back on afterwards and carry on driving. Same for fixed buckets in a road car, steering wheels with no airbag, decats etc. Not illegal, but will fail an MOT. You will fail an MOT if the speedo isn't reading correctly, which may be caused by rolling radius issues, but that doesn't make running tyres >3% bigger illegal. Quote Link to comment Share on other sites More sharing options...
longsh07 Posted October 26, 2016 Author Share Posted October 26, 2016 I'm sure with the dice returned, technically your car would no longer be road worthy. It's the same principle as passing an MOT with cats fitted then immediately removing them right? If you were to get pulled over and really pi**ed on the coppers chips I'm sure they would find every reason possible to say your car is no longer road worthy because it cant pass an MOT right this minute. No MOT = no insurance (specialist insurance aside of course). Quote Link to comment Share on other sites More sharing options...
BobbyZ Posted October 26, 2016 Share Posted October 26, 2016 Apparently it's part of an MOT Hi MattStandard mot test covers this but a lot of cars get through with "wrong" tyres if all 4 are the same by all means call to discuss as there are some benefits to using a smaller rolling radius but larger rolling radius will - make speedo read slow - reduce acceleration and top speed through longer gearing - reduce brake effectiveness Sent from my HTC One M9 using Tapatalk You should defo give them a call to get an explanation on how longer gearing would reduce your top speed. Quote Link to comment Share on other sites More sharing options...
Flex Posted October 26, 2016 Share Posted October 26, 2016 Curly Wurlys are awful, get past the good bit and your left with bloody toffee sticking to your teeth. Quote Link to comment Share on other sites More sharing options...
longsh07 Posted October 26, 2016 Author Share Posted October 26, 2016 Last reply from them: If anything it should say 0% the rolling radius must be the same as originally fitted. I was given this info by various tyre suppliers. Might be best to phone the government. Certainly speedo error would eventually cause the biggest issue. Anyway as long as you are only reducing radius can't see it being an issue.Certainly I've made track cars a lot quicker by going well under. Not going to follow up with them any more on this. Quote Link to comment Share on other sites More sharing options...
docwra Posted October 26, 2016 Share Posted October 26, 2016 Who are these jokers? What do they do when someone rolls in with a 350Z, check the chassis number to check whether it had 17's, 18's or 19's as standard? Do they point blank refuse to MoT anything with aftermarket wheels on, as they dont know what the OE sizes were? Can someone tell me how does a smaller radius tyre reduce brake efficiency as well? Quote Link to comment Share on other sites More sharing options...
longsh07 Posted October 26, 2016 Author Share Posted October 26, 2016 Who are these jokers? What do they do when someone rolls in with a 350Z, check the chassis number to check whether it had 17's, 18's or 19's as standard? Do they point blank refuse to MoT anything with aftermarket wheels on, as they dont know what the OE sizes were? Can someone tell me how does a smaller radius tyre reduce brake efficiency as well? Link to their site is in the first post. Needless to say I wont be buying anything from them. Quote Link to comment Share on other sites More sharing options...
Ekona Posted October 26, 2016 Share Posted October 26, 2016 No MOT = no insurance (specialist insurance aside of course). Nonsense. How many times does this come up still?? You're totally insured, however you may well find the insurer will reduce your payout if you write the car off. MOT fail != unroadworthy. Do you have a crack in your windscreen? Or a chip over the size of a pound? Do you still drive your car? How about if your numberplate fell off, could you drive your car home? How about if the numberplate didn't have the supplier on, or a non-spec flag (like a Nissan logo)? Or if the spare tyre was completely bald? Exactly. It's bobbins of the highest bobbinity. Not having a pop at you fella, all of this said with a casual winky smile as you'll sit back and realise how daft the regs are. Quote Link to comment Share on other sites More sharing options...
Ekona Posted October 26, 2016 Share Posted October 26, 2016 Curly Wurlys are awful, get past the good bit and your left with bloody toffee sticking to your teeth. We can't be friends any more. Sorry. Quote Link to comment Share on other sites More sharing options...
brillomaster Posted October 26, 2016 Share Posted October 26, 2016 Apparently it's part of an MOT Hi MattStandard mot test covers this but a lot of cars get through with "wrong" tyres if all 4 are the same by all means call to discuss as there are some benefits to using a smaller rolling radius but larger rolling radius will - make speedo read slow - reduce acceleration and top speed through longer gearing - reduce brake effectiveness Sent from my HTC One M9 using Tapatalk You should defo give them a call to get an explanation on how longer gearing would reduce your top speed. most cars top speeds are limited by air resistance and engine power, not the gearing (very few cars can hit maximum rpm in top gear, the gearing is optimised for economy whilst cruising). anything that lengthens the gearing will make it harder for a car to reach its maximum speed, and ultimately, that maximum speed will be slightly lower. EDIT: unless you lengthen the gearing so much that the top speed is now reached in maximum rpm in 5th gear, rather than midway through 6th gear, in which case the top speed might go up a tad (though it will take longer to get there) Quote Link to comment Share on other sites More sharing options...
longsh07 Posted October 26, 2016 Author Share Posted October 26, 2016 No MOT = no insurance (specialist insurance aside of course). Nonsense. How many times does this come up still?? You're totally insured, however you may well find the insurer will reduce your payout if you write the car off. MOT fail != unroadworthy. Do you have a crack in your windscreen? Or a chip over the size of a pound? Do you still drive your car? How about if your numberplate fell off, could you drive your car home? How about if the numberplate didn't have the supplier on, or a non-spec flag (like a Nissan logo)? Or if the spare tyre was completely bald? Exactly. It's bobbins of the highest bobbinity. Not having a pop at you fella, all of this said with a casual winky smile as you'll sit back and realise how daft the regs are. No worries Dan, I realise your not having a pop No MOT = No insurance was misleading to be fair. Poor choice of words on my part but was more for speed than accuracy. My policy does say I have to maintain the car in a road worthy condition and have an MOT certificate if required or it might affect my right to claim. As for how daft the regs are I'm all to aware as I'm sure you know from posting in my R90 thread a minute ago lol Quote Link to comment Share on other sites More sharing options...
Flex Posted October 26, 2016 Share Posted October 26, 2016 Curly Wurlys are awful, get past the good bit and your left with bloody toffee sticking to your teeth. We can't be friends any more. Sorry. There's so much more confectionery out there, I know we can find common ground and make it work. I do love a boost bar, especially when hungover. Quote Link to comment Share on other sites More sharing options...
coldel Posted October 26, 2016 Share Posted October 26, 2016 Boost Bars are teeth pullers! And Curly Wurlys are definitely getting smaller... 1 Quote Link to comment Share on other sites More sharing options...
docwra Posted October 26, 2016 Share Posted October 26, 2016 Curly Wurlys are awful, get past the good bit and your left with bloody toffee sticking to your teeth. We can't be friends any more. Sorry. Result 1 Quote Link to comment Share on other sites More sharing options...
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