+1 riding with no hands is not a reliable way. Road crown alone can give a wrong impression. If that is your only viable way then find the flattest piece of pavement, a playground might be a good option. The down and dirty home-brew way is to "string" the bike and take measurements. If the seller gets miffed at you stringing the bike, maybe yoiu shouldn't be buying that bike. If they have nothing to hide they should not object.
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Last edited by drlogik; 04-09-21 at 07:04 AM.