hymer1942 Posted October 18, 2013 Share Posted October 18, 2013 Morning all, a question for the bright sparks. If I put bigger tyres ón the Real axle giring a 7% reduktion in revolutions Per mile what Can I Expect in duel saving. Or am I totally ón the Wrongwave length. Barrie Link to comment Share on other sites More sharing options...
Tracker Posted October 18, 2013 Share Posted October 18, 2013 Probably nothing! Or at least not measurable in view of all the other variables. However larger tyres do tend to improve the ride a bit and that alone may be worth the effort? Bigger tyres can also increase the payload but for that you need to seek advice and maybe replate via SVTech and the DVLA HOWEVER - different sizes front and rear could make the spare illegal if the tyres on each axle are not the same size, so if you want to change consider changing all 5. Don't forget to tell your insurers who will probably not charge any extra premium but may charge you one of their favourites - a 'service charge' - for the 'work' involved of noting it on your policy records! Link to comment Share on other sites More sharing options...
ham Posted October 18, 2013 Share Posted October 18, 2013 hymer1942 - 2013-10-18 10:46 AM Morning all, a question for the bright sparks. If I put bigger tyres ón the Real axle giring a 7% reduktion in revolutions Per mile what Can I Expect in duel saving. Or am I totally ón the Wrongwave length. Barrie If you are putting small or Bigger tyres on and the diameter of the tyre changes . would you not have to get the milometer recalibrated? Here’s the basic issue: Your speedometer, odometer, traction control, torque and gearing settings are all based on the distance that your tyre travels over one complete revolution, which is determined by the outside diameter of the tyre-and-wheel assembly. A tyre with a different outside diameter will travel a different distance over that one revolution with a different amount of torque. So, when changing the diameter of your rims, you must make sure that the new wheel and tyre assembly keeps the same overall diameter as the old, or your speedometer will be showing you the wrong speed and your traction control settings will be off. This becomes confusing, because tyre sizes are measured by the inside diameter, that is, an R17 tyre is sized to fit onto a rim with a 17” outside diameter. The outside diameter of the tyre, also known as the standing height is determined by how much sidewall it has, called the aspect height In order to keep the same outside diameter, when you gain an inch of rim size, say, from 17” to 18”, you must lose an inch in the standing height of the tire, and vice versa. This is why 22”or 24” rims have those low-profile tyres that look like thick rubber bands. To determine the proper size requires a bit of maths, because the aspect height is expressed in tyre sizes as a percentage of the width, CONFUSING OR WHAT. do you mean different size tyres on the rear to the front in physical size, if so I think you will find its a NO NO Link to comment Share on other sites More sharing options...
Tracker Posted October 18, 2013 Share Posted October 18, 2013 As most speedos are already around 5% over optimistic anyway, personally I would be happy with a 7% increase in rolling circumference but would check it against the sat nav on longish straights at a constant speed just so that i knew what the true speed is at an indicated 30,40,50,60,and 70 mph. There are several tyre sellers websites that enable one to enter wheel and tyre sizes for comparison - this is just one such site - http://www.blackcircles.com/?gclid=CNeAnqWmoLoCFWfLtAodk1cAHw Link to comment Share on other sites More sharing options...
laimeduck Posted October 18, 2013 Share Posted October 18, 2013 I assume that your motorhome is rear wheel drive? If not, unless you put the larger tyres on the front wheels, you will gain nothing. As has been said you should change the size on all 4 wheels & the spare. If you know the size of tyre you want to go up to you can use this calculator http://tire-size-conversion.com/speedometer-calibration/ The other concern is will the larger tyre fit not only in the wheel housing without rubbing, but will you be able to use full lock without the wheel rubbing? (I have looked at this for my Honda CRV as it seems to be too low geared & this could be a solution) Link to comment Share on other sites More sharing options...
hymer1942 Posted October 18, 2013 Author Share Posted October 18, 2013 Rear wheel Mercedes sprinter, low geared is another reason to try and of course bigger tyres give better stability. So am foring from 195/70. To 205/70 which fit fine and look better. Barrie Link to comment Share on other sites More sharing options...
Overdrive Posted October 19, 2013 Share Posted October 19, 2013 Both are a 70 profile so no change in circumference! Just need to ensure you have enough clearance in the wheel arch. David Link to comment Share on other sites More sharing options...
Billggski Posted October 19, 2013 Share Posted October 19, 2013 Sorry, the 70 is the ratio of the width to the height, so a 205-70 has a bigger circumference than a 195-70. My jaguar has different sizes front and back with a space saver spare that is not the same as either! If it's original equipment there is no issue. Changes wheel sizes isn't much of a problem as I have smaller wheels (but higher aspect ratio) for the winter tyres. Link to comment Share on other sites More sharing options...
Tracker Posted October 19, 2013 Share Posted October 19, 2013 Overdrive - 2013-10-19 9:56 AM Both are a 70 profile so no change in circumference! Just need to ensure you have enough clearance in the wheel arch. David Unless I have got it all wrong, as I understand it the 195 & 205 refer to the tyre width in mm and the 70 refers to the depth of the tyre as a percentage of it's width. On that basis a 205 tyre is 10 mm wider than a 195 tyre and it follows that 70% of 205 (143.5mm) is a little bit more of a diameter than 70% of 195 (136.5) - 7 mm extra diameter - or 3.5 mm greater all round (at each side and top and bottom!) In reality it will make little difference to the speedo reading - probably about 1.5 mph more at a true 60 mph (ie 61.5 mph) but as modern speedos all over read anyway it will not really matter in the real world. However as stated, clearance on some van wheel arches is tight, especially when changing a wheel, and that might well be a factor. Link to comment Share on other sites More sharing options...
hymer1942 Posted October 19, 2013 Author Share Posted October 19, 2013 Thanks all job done looks good frels good. Barrie, and have fitted BF GOODRICH ACTIVAN not Cheap but good reportage. Barrie Link to comment Share on other sites More sharing options...
Brambles Posted October 19, 2013 Share Posted October 19, 2013 Tracker. The tyre wall is 7mm more, so that is twice that on the diameter. 14mm increased diameter. Link to comment Share on other sites More sharing options...
Tracker Posted October 19, 2013 Share Posted October 19, 2013 Brambles - 2013-10-19 4:06 PM Tracker. The tyre wall is 7mm more, so that is twice that on the diameter. 14mm increased diameter. I wondered whether you would spot my deliberate mistake Sargeant Wilson!! Yeah but, no but, yeah but, it's still 7 mm each side and top and bottom!! Link to comment Share on other sites More sharing options...
Brambles Posted October 19, 2013 Share Posted October 19, 2013 15 inch wheel say. 195/70 tyre ........ 381 + (2 x 136.5) = 654mm dia 205/70 tyre ........ 381 + (2 x 143.5) = 668mm dia. Circumference = 2053.6 and 2097.5 difference = 2.14%. Do not know where the OP's 7% comes from. Link to comment Share on other sites More sharing options...
Brambles Posted October 19, 2013 Share Posted October 19, 2013 Tracker - 2013-10-19 4:15 PM Brambles - 2013-10-19 4:06 PM Tracker. The tyre wall is 7mm more, so that is twice that on the diameter. 14mm increased diameter. I wondered whether you would spot my deliberate mistake Sargeant Wilson!! Yeah but, no but, yeah but, it's still 7 mm each side and top and bottom!! so where does your halving to get 3.5mm come from.? Link to comment Share on other sites More sharing options...
Tracker Posted October 19, 2013 Share Posted October 19, 2013 Brambles - 2013-10-19 4:20 PM so where does your halving to get 3.5mm come from.? Mathematics was always an UPhill struggle for me, and add that to a senior moment or three and as far as I know 2 = 2 + 5!! Link to comment Share on other sites More sharing options...
Brambles Posted October 19, 2013 Share Posted October 19, 2013 ...I am just waiting for someone to show my calcs are wrong and I too am having a senior moment. Link to comment Share on other sites More sharing options...
Brambles Posted October 19, 2013 Share Posted October 19, 2013 oops, double clicked submit. Link to comment Share on other sites More sharing options...
hymer1942 Posted October 19, 2013 Author Share Posted October 19, 2013 Hi all I thought the circumference was 7% ish. Barrie Link to comment Share on other sites More sharing options...
laimeduck Posted October 19, 2013 Share Posted October 19, 2013 Brambles - 2013-10-19 5:03 PM ...I am just waiting for someone to show my calcs are wrong and I too am having a senior moment. Nope, you are spot on! :-D :-D .....and you can check this against the speedo difference calculator http://tire-size-conversion.com/speedometer-calibration/ ......... which gives an identical % difference of 2.14% (or 1.28mph at 60mph) If you also increased the aspect ration from say 70 to 80 ie 205/80/R15 then the difference is more significant at 8.3% or 5 mph at 60mph. This is what I was looking to do on my Honda CRV which I think is geared too low & I suspect what the OP was thinking of. (Just changing the aspect ratio from say 70 to 80 will increase the % more than changing the width of the tyre ...... ie a tyre of 195/80/R15 will give an increase of 5.96% or 3.58 mph at 60mph) Link to comment Share on other sites More sharing options...
hymer1942 Posted October 20, 2013 Author Share Posted October 20, 2013 Correct in What you say but 195/80/15 is fine, a 205/80/15 not to be had, which is what I would have liked. Barrie Link to comment Share on other sites More sharing options...
Brambles Posted October 20, 2013 Share Posted October 20, 2013 How about 215/70R15 if you rims and arch clearance etc wil take it? Link to comment Share on other sites More sharing options...
hymer1942 Posted October 20, 2013 Author Share Posted October 20, 2013 Yes considered that Brambles , but twin wheeled rear those leave to narrower gap between tyres. Barrie Link to comment Share on other sites More sharing options...
OutBout Posted August 6, 2014 Share Posted August 6, 2014 Hi, i'm maybe well too late to add any help but you could give the guy who owns this tyre company in Belfast a call. I've heard he knows everything there is to know about vehicle tyres. Good luck. Link to comment Share on other sites More sharing options...
Brambles Posted August 6, 2014 Share Posted August 6, 2014 OutBout - 2014-08-06 11:05 AM Hi, i'm maybe well too late to add any help but you could give the guy who owns this tyre company in Belfast a call. I've heard he knows everything there is to know about vehicle tyres. Good luck. ...and that is because you are that company. Link to comment Share on other sites More sharing options...
Archiesgrandad Posted August 6, 2014 Share Posted August 6, 2014 Now that we know that the van in question isn't a Fiat based jobby, I feel free to point out the following:- A team of highly qualified auto engineers, assisted as required by a team of skilled tyre technicians, acting on behalf of one of the most successful and highly regarded motor manufacturers the world has ever known, worked out what would be the best tyres on the van you own. I'm not saying that you don't know better, but I think the odds are against it, and although I've been in the transport business for more than 30 years, I'm not aware of any real problems in this respect. I do recall a notice that hung on the wall of a motor repair workshop owned by a friend:- Labour Charge £50 per hour Labour Charge with customer watching £60 per hour Labour Charge with customer helping £70 per hour I also recall from my time as an engineer with a large motor manufacturer that we frequently complained that whilst making things fool proof was easy, making things clever proof was much harder. AGD Link to comment Share on other sites More sharing options...
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