Wobbly Speedometer Help?

[SquareBody86]

I noticed that whenever I drive Ol' Rusty (1986 C10 Silverado) around the yard the speedo seems to the 'wobbling' as it registers the speed, its not bouncing around like crazy as the needle is moving like it should but it wobbles back and forth as it goes making it difficult to tell the actual speed while going along. I'm thinking it might be a worn out speedo gear or cable oh and how do you do the math to get yourself the correct tooth gear? Rusty originally came with 205/75r/15's where as I currently have 235/75r/15's (gives it a bit more ground clearance) so would the bigger tire affect the speedo much?

[zieg85]

Wobble is usually a speedometer cable.  Tire size increase will just make the speedometer read slow.  A tire jump from 205's to 235's would be 5-6% slow.  Showing 60 may actually be 63-64 mph.  There are free speedometer apps for smart phones.

[LTZ C20]

Uhhh, 205 and 235 are the width of the tire. 75 is the height. Jumping from 205 to 235 only changes the foot print of the tire. Wheel height and rim diameter change speedometer accuracy. If you jumped from 75 to 85 or to 55 OR of jumped from a 15 in rim to a 16 or a 20 inch rim, then speedometer gears would need to be changed. Only tire height and rim diameter change accuracy. Tire width just puts more rubber touching the pavement.

[zieg85]

Uhhh, 205 and 235 are the width of the tire. 75 is the height. Jumping from 205 to 235 only changes the foot print of the tire. Wheel height and rim diameter change speedometer accuracy. If you jumped from 75 to 85 or to 55 OR of jumped from a 15 in rim to a 16 or a 20 inch rim, then speedometer gears would need to be changed. Only tire height and rim diameter change accuracy. Tire width just puts more rubber touching the pavement.

205's are much shorter than 235's.  75 is the width... sorry

[SquareBody86]

Uhhh, 205 and 235 are the width of the tire. 75 is the height. Jumping from 205 to 235 only changes the foot print of the tire. Wheel height and rim diameter change speedometer accuracy. If you jumped from 75 to 85 or to 55 OR of jumped from a 15 in rim to a 16 or a 20 inch rim, then speedometer gears would need to be changed. Only tire height and rim diameter change accuracy. Tire width just puts more rubber touching the pavement.

205's are much shorter than 235's.  75 is the width... sorry

Yeah, I was about to say lol the guy I got Rusty from had 205's on the front giving him a hot rod stance, didn't look bad but I swapped back to 235's all around, right so 3-4mph off? I can compensate for that, I'll have to see how it goes once on the road.

[LTZ C20]

205's are much shorter than 235's.  75 is the width... sorry

Not sure who your talking to Zieg. Me or the OP.

To the OP, tire measurements using the metric standard, the way you listed, (205/75/15).

205 - is the width of the tire (in millimeters) across the middle of the tread area, sidewall to sidewall.

75 - is the aspect ration, which overall relates to the height of the tire from the bead seat to the tread area.

15 - rim diameter in inches.

Measuring a tire width in the standard format (33x8 - 15) yields  different measurement which isn't anything you need to worry about as you listed your tires in the metric format.

Think of it like this. 205 being the width would be like the width of your foot from your big toe to your pinky toe. It does not  affect your foot length, just how wide your foot print is. 75 would be your foot length from toe tips to heel. That being shorter or longer changes how much distance one step would cover.

[zieg85]

205's are much shorter than 235's.  75 is the width... sorry

Not sure who your talking to Zieg. Me or the OP.

To the OP, tire measurements using the metric standard, the way you listed, (205/75/15).

205 - is the width of the tire (in millimeters) across the middle of the tread area, sidewall to sidewall.

75 - is the aspect ration, which overall relates to the height of the tire from the bead seat to the tread area.

15 - rim diameter in inches.

Measuring a tire width in the standard format (33x8 - 15) yields  different measurement which isn't anything you need to worry about as you listed your tires in the metric format.

Think of it like this. 205 being the width would be like the width of your foot from your big toe to your pinky toe. It does not  affect your foot length, just how wide your foot print is. 75 would be your foot length from toe tips to heel. That being shorter or longer changes how much distance one step would cover.

I stand corrected in the tire jargon as I just looked it up.  Don't understand it but I read it.  From experience I know a 235 75 is much taller than a 205 75.  If you put a 235 70 next to a 225 75 they will be about the same height only the 235 70 will be wider.  Before the numbers there were letters on passenger tires, the 235's used to be L's.  G78-15 was about a 215 and the H78 were about the 225's.  A buddy used to run N-50's on the rear of his Chevelle with G70's up front and they were about the same height.   

[LTZ C20]

It's ok.

[VileZambonie]

75% of 205 = 153.75

75% of 235 = 176.25

So yes it will be taller but you were reading them wrong

[Irish_Alley]

i was going to say i thought the middle number was a percentage not a actual number to height. i tried to have a tire shop explain to me how it worked but he said it was too confusing and wouldnt go into detail

[bd]

I noticed that whenever I drive Ol' Rusty (1986 C10 Silverado) around the yard the speedo seems to be 'wobbling' as it registers the speed, its not bouncing around like crazy as the needle is moving like it should but it wobbles back and forth as it goes making it difficult to tell the actual speed while going along. I'm thinking it might be a worn out speedo gear or cable....

Common causes of "bouncy" speedometer needles

[blazer74]

I noticed that whenever I drive Ol' Rusty (1986 C10 Silverado) around the yard the speedo seems to the 'wobbling' as it registers the speed, its not bouncing around like crazy as the needle is moving like it should but it wobbles back and forth as it goes making it difficult to tell the actual speed while going along. I'm thinking it might be a worn out speedo gear or cable oh and how do you do the math to get yourself the correct tooth gear? Rusty originally came with 205/75r/15's where as I currently have 235/75r/15's (gives it a bit more ground clearance) so would the bigger tire affect the speedo much?

Had the bouncing speedo. Would vary back and forth relative to actual speed.

Would make a snap sound each time it cycled. Lubed then replaced the cable assy with no help. Ended up being the speedo itself.